1. Field of the Invention
The present invention relates to a DC/DC bridge for controlling a direct-current load, said bridge having a power stage provided with controllable semiconductor switches and comprising two bridge sections, one of which bridge sections conducts direct current while the other one is controlled via PWM to regulate the current magnitude.
2. Discussion of the Background Art
Elevator motor drives may be either alternating-current or direct-current motor drives. The drives may be controlled e.g. via PWM (Pulse Width Modulation). Today, alternating-current motor drives are fairly common, especially because of the simple construction of alternating-current motors. However, direct-current motor drives are still in use. It is not always appropriate to replace a direct-current motor drive with an alternating-current motor drive, because e.g. gearless direct-current motor drives and the direct-current motors used in them are durable, and it is therefore unnecessary to replace them with alternating-current motor drives. Besides, replacing the motor entails relatively high costs.
Since the trend is towards alternating-current motor drives, it is also hardly rational to specifically develop power electronics systems for use in the control of direct-current drives. In addition, semiconductor components, such as IGBTs, used in alternating-current drives are becoming increasingly efficient and economical. Moreover, it is to be expected that new regulations concerning network harmonics may result in future use of traditional thyristor bridges used in direct-current drives becoming more difficult.